bug#44503: 27.1; image-scroll-up and image-scroll-down

[Roland Winkler]

My understanding of the doc strings of image-scroll-up and
image-scroll-down is that the argument N should be a number, nil, or
`-'."  However, these commands use (interactive "P") with
prefix-numeric-value inside the body of these commands.  I suggest
to document this behavior.  (I guess it is not very clean to use
prefix-numeric-value inside the body of these commands.  But
changing this behavior likely will break existing code that uses
these commands.)

I realized this when I looked at doc-view's scrolling commands
doc-view-scroll-up-or-next-page and
doc-view-scroll-down-or-previous-page
that likewise use (interactive "P"), contrary, to what the
docstrings of these commands say, and I was surprised that this
gives a meaningful behavior.  So these docstrings probably should be
updated, too.


In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2020-08-31 built on regnitz
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description: Ubuntu 16.04.7 LTS